Ebullient cooling device

ABSTRACT

An ebullient cooling device having a simple structure and capable of limiting the bubbles to an appropriate volume. The ebullient cooling device for cooling a heat generating element is provided with a plurality of vertically arranged cooling channels comprising a lower channel ( 2 ), a middle channel ( 3 ) and un upper channel ( 4 ). Each cooling channel has cooling fins ( 12 ) for guiding a refrigerant to flow in a vertical direction, and a vapor discharge path ( 16 ) formed at the side of the cooling fins ( 12 ) that is opposite the side in contact with the heat generating element. Furthermore, flow path partition/vapor discharge guiding plates ( 18 ) are provided between the cooling channels so that the bubbles that have been generated are guided to the vapor discharge path ( 16 ) and prevented from moving into the subsequent cooling channel.

TECHNICAL FIELD

The present invention relates to an ebullient cooling device, and moreparticularly to an improvement in cooling performance of a coolingdevice using boiling two-phase flow (gas-liquid two-phase flow).

BACKGROUND ART

Conventionally, cooling devices using boiling two-phase flow under aforced flow have been developed and applied to inverter cooling systemsof hybrid vehicles and others.

Patent Document 1 discloses a power semiconductor module which isstructured with a cooling base including a coolant flow path and aplurality of power semiconductors mounted on the base. The coolingefficiency is improved by determining an appropriate mounting positionof power semiconductor element to optimize the temperature increase ofcoolant.

Patent Document 2 discloses an ebullient cooling device which preventsdeterioration of heat dissipation performance at an upper portion(downstream region) of a module. Vapor generated at a lower portion(upstream region) of the module due to heat received from a powersemiconductor is prevented from entering into the upper portion(downstream region) of the module by a partition or the like.

PRIOR ART DOCUMENT Patent Documents

Patent Document 1: JP 2007-12722A

Patent Document 2: JP 9-23081A

DISCLOSURE OF THE INVENTION Objects to be Achieved by the Invention

It is required for cooling devices using boiling two-phase flow to bedesigned not only to restrict a decrease of critical heat flux and heattransfer coefficient at the time of boiling, but also to be compact aspossible. Generally, the heat transfer performance during boiling isdetermined based on gas-liquid behavior at the bottom-of bubbles. Morespecifically, two types of regions coexist, one region where the heattransfer is enhanced because a thin liquid film is formed, and the otherregion where the heat transfer is deteriorated due to a development ofdried portions. The size of the area where bubbles are attachedsignificantly influences which of the regions will be dominating. Whenthe size of the bubble attaching area is enlarged as the bubbles grow,the dominating region may be changed from the heat transfer enhancingregion to the deteriorating region.

FIGS. 8A and 8B show a heat transfer manner when a heat transferenhancement is low in a nucleate boiling heat transfer as a small bubblegrows. Shown is a case where an open flow path is used and the size of abubble is small. FIG. 8(A) is a plan view; and FIG. 8(B) is a side view.When the pressure is lower, the size of a bubble is larger. The lowerthe temperature of ambient fluid is than the saturation temperature(sub-cool state), the smaller the size of a bubble. When the size of abubble is small, although the area of dried portion 50 is accordinglysmall, the area occupied by a thin liquid film 52 also becomes small. Asa result, the boiling heat transfer effect is weakened, while a heattransfer applied to a liquid single-phase flow surrounding the bubbleremains large. Therefore, the ratio of heat transfer enhancement issmaller than the heat transfer to the liquid single-phase flow.

FIGS. 9A and 9B show a heat transfer manner when the heat transferenhancement is high in a nucleate boiling heat transfer as a largebubble grows. Shown is a case where an open flow path is used and thesize of a bubble is middle to large. When the bubble size becomeslarger, although the area of the dried portion 50 becomes large, thearea occupied by the thin liquid film 52 also becomes large. As aresult, the effect of the boiling heat transfer becomes significant, andas a result the ratio of heat transfer enhancement is larger than theheat transfer to the liquid single-phase flow.

FIGS. 10A and 10B show a manner in which a heat transfer is deterioratedin a nucleate boiling heat transfer as a massive bubble grows. Shown isa case where an open flow path is used and the size of a bubble issignificantly large. When a bubble becomes excessively large, the areaoccupied by the dried portion 50 expands. Thus, the heat transferdeterioration of this area becomes more significant than the heattransfer enhancement achieved by the evaporation of the thin liquid film52. As a result, an aspect of deterioration of heat transfer becomesobvious in the heat transfer area as a whole.

FIGS. 11A and 11B show a manner in which a heat transfer is enhanced ina nucleate boiling heat transfer as a flattened bubble grows betweencooling fins 12 (hereinafter to referred simply as “fins”). Shown is acase where a narrow flow path between fins is used and the size of abubble is medium. Increase of both the heat transfer area and heattransfer coefficient with the fins 12 can be achieved by generating andgrowing a flattened bubble of a sufficient size.

FIG. 12 shows a relationship between a bubble volume and heat transferenhancement/deterioration. The horizontal axis shows a bubble volume,while the vertical axis shows the heat transfer characteristics. Thearrow P of the vertical axis indicates enhancement of the heat transfer,while the arrow Q indicates deterioration of the heat transfer. Both inan open flow path (indicated by sign “a” in the drawing) and a narrowflow path between fins (indicated by sign “b” in the drawing), heattransfer enhancement cannot be expected when the bubble volume is eithertoo small or too large. It is necessary to maintain bubbles at asufficient size (the optimum volume is shown by “OPT” in the drawing).Therefore, it is important to control a time duration when a bubblecontacts with a heat transfer surface in order to prevent the contacttime from being excessively long.

Means for Achieving the Objects

An object of the present invention is to provide a cooling device whichmaintains a bubble volume at a sufficient size with a simple structure,and thereby enhances heat transfer characteristics.

The present invention is characterized by an ebullient cooling devicefor cooling a heating body, comprising: at least first and secondcooling channel blocks, both arranged in a vertical direction,comprising: a cooling fin that causes coolant to flow in the verticaldirection; and a vapor discharge path formed on a side of the coolingfin that is opposite to a side in contact with a heating body; and aguiding portion provided between the first and second cooling channelblocks, the guiding portion guiding a bubble generated in the firstcooling channel block to the vapor discharge path by preventing thebubble from proceeding into the second cooling channel block.

In one embodiment of the present invention, the ebullient cooling devicefurther comprises a partition positioned between the cooling fin and thevapor discharge path, and the guiding portion is formed as a portion ofthe partition.

In another embodiment of the present invention, the partition has anopening portion at a position between the first and second coolingchannel blocks, and the guiding portion is formed to project from anedge of the opening portion towards the heating body contacting side ofthe cooling fin.

In yet another embodiment, the ebullient cooling device furthercomprises a fluid supply pipe that is provided between the first andsecond cooling channel blocks, the fluid supply pipe supplying thecoolant to the second cooling channel block, and a front edge of theguiding portion contacts with the fluid supply pipe.

In yet another embodiment, the first cooling channel block is positionedvertically beneath the second cooling channel block, and the guidingportion is formed, from the cooling fin of the second cooling channelblock, to be tilted towards the cooling fin of the first cooling channelblock.

Effects of the Invention

The present invention can improve heat transfer characteristics bymaintaining a bubble volume at a sufficient size with a simplestructure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a front view of a cooling device according to an embodimentof the present invention.

FIG. 1B is a side view of a cooling device according to an embodiment ofthe present invention.

FIG. 1C is a cross-sectional view taken along the line B-B′ of a coolingdevice according to an embodiment of the present invention.

FIG. 1D is a cross-sectional view taken along the line A-A′ of a coolingdevice according to an embodiment of the present invention.

FIG. 2A is a design diagram of a fluid supply pipe.

FIG. 2B is another design diagram of a fluid supply pipe.

FIG. 3A is a front view of a flow path partition/vapor discharge guidingplate.

FIG. 3B is a side view of a flow path partition/vapor discharge guidingplate.

FIG. 4 is an exploded perspective view of fins and a flow pathpartition/vapor discharge guiding plate.

FIG. 5 is an overall design diagram of a cooling device according to anembodiment of the present invention.

FIG. 6 is a system configuration diagram according to an embodiment ofthe present invention.

FIG. 7 is a system configuration diagram according to another embodimentof the present invention.

FIG. 8A is a plan view showing heat transfer characteristics when anopen flow path is used and the size of a bubble is small.

FIG. 8B is a side view showing heat transfer characteristics when anopen flow path is used and the size of a bubble is small.

FIG. 9A is a plan view showing heat transfer characteristics when anopen flow path is used and the size of a bubble is medium.

FIG. 9B is a side view showing heat transfer characteristics when anopen flow path is used and the size of a bubble is medium.

FIG. 10A is a plan view showing heat transfer characteristics when anopen flow path is used and the size of a bubble is excessively large.

FIG. 10B is a side view showing heat transfer characteristics when anopen flow path is used and the size of a bubble is excessively large.

FIG. 11A is a plan view showing heat transfer characteristics when anarrow flow path between fins is used and the size of a bubble ismedium.

FIG. 11B is a side view showing heat transfer characteristics when anarrow flow path between fins is used and the size of a bubble ismedium.

FIG. 12 is a graph showing a relationship between a bubble volume andheat transfer characteristics.

REFERENCE NUMERALS

1 ebullient cooling device, 2 lower channel block, 3 middle channelblock, 4 upper channel block, 10 fluid supply pipe, 12 fins, 13 finbase, 14 cooling surface, 16 vapor discharge path, 18 flow pathpartition/vapor discharge guiding plate, 19 guiding portion, 20partition.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments according to the present invention are described below byreferring to the attached drawings.

FIGS. 1A to 1D show a structure of main elements of an ebullient coolingdevice according to an embodiment of the present invention. FIG. 1 is aplan view; FIG. 1B is a side view; FIG. 1C is a cross-sectional viewtaken along the line B-B′; and FIG. 1D is a cross-sectional view takenalong the line A-A′.

The ebullient cooling device 1 comprises a fluid supply pipe 10, fins12, fin base 13, cooling surface 14, vapor discharge path 16, and flowpath partition/vapor discharge guiding plate 18.

A plurality of the fins 12 are provided to stand on the fin base 13 atpredetermined intervals. A multi-channel system is provided in whichfins 12 form cooling channels. As shown in the front view in FIG. 1A,the ebullient cooling device 1 is installed in a vertical direction(vertical installation) with each fin 12 arranged to extend in thevertical direction. FIG. 1A shows an example structure in which a lowerchannel block 2, middle channel block 3, and upper channel block 4 areprovided, each of which is further divided by a partition 20 into rightand left blocks, resulting in 6 channel blocks in total. However, theprevent invention is not limited to this example. Each fin 12 is madeof, for example, aluminum having a high heat conductivity. Coolant flowpaths are formed in a vertical direction. The coolant isforce-circulated upward in the vertical direction by a pump. The fins 12expand the surface area of the fin base 13 which forms the coolingsurface 14 and also enhances the heat conductivity. The cooling surface14 of the fins 12 is contacted by, for example, a power device unit(IGBT module) of a hybrid vehicle.

Being positioned between blocks of fins 12, the fluid supply pipe 10supplies cooling fluid as coolant to the fins 12. As shown in FIG. 1A,the fluid supply pipe 10 is provided, in a horizontal direction, foreach of the channel blocks. To the lower channel block 2, the coolant issupplied upward from the fluid supply pipe 10 positioned beneath thelower channel block 2; to the middle channel block 3, the coolant issupplied upward from the fluid supply pipe 10 positioned beneath themiddle channel block 3, that is between the middle channel block 3 andthe lower channel block 2; and to the upper channel block 4, the coolantis supplied upward from the fluid supply pipe 10 positioned beneath theupper channel block 4, that is between the upper channel block 4 and themiddle channel block 3. As described above, the fluid supply pipe 10 ispositioned in a horizontal direction. The coolant is supplied from theright side as shown by arrows in FIG. 1A to each of fluid supply pipes10 which are positioned on the right side of the partition 20, while thecoolant is supplied from the left side to each of fluid supply pipes 10which are positioned on the left side of the partition 20. The coolantis heated and boiled by the fins 12 of each channel block and bubblesare generated.

The vapor discharge path 16 is provided on the top surface side of thefins, that is, the surface opposite to the cooling surface 14 of thefins 12 in contact with a heating body. Being commonly provided for allof the cooling channel blocks, the vapor discharge path 16 dischargesbubbles generated in each of the cooling channel blocks.

The flow path partition/vapor discharge guiding plate 18 is provided onthe top surface of the fins 12, that is the surface opposite to the finbase 13. In other words, the flow path partition/vapor discharge guidingplate 18 is provided to contact with the surface opposite to the coolingsurface of the fins 12 in order to partition between the fins 12 and thevapor discharge path 16. Further, the flow path partition/vapordischarge guiding plate 18 is provided with an opening portion betweenthe fins 12 of the lower channel block 2 and fins 12 of the middlechannel block 3, and the other opening portion between the fins 12 ofthe middle channel block 3 and the fins 12 of the upper channel block 4.Furthermore, the flow path partition/vapor discharge guiding plate 18includes, at the edge of the opening portion, a guiding portion 19 whichprojects to be tilted at a certain angle towards the fin base 13. Asshown in FIG. 1B, it should be noted that between the lower channelblock 2 and the middle channel block 3, the guiding portion 19 of theflow path partition/vapor discharge guiding plate 18 projects towardsthe fin base 13 from the vertically lower portion of the fins 12 of themiddle channel block so as to contact with the fluid supply pipe 10.Similarly, between the middle channel block 3 and the upper channelblock 4, the guiding portion 19 projects towards the fin base 13 fromthe vertically lower portion of the fins 12 of the upper channel block 4so as to contact with the fluid supply pipe 10. The guiding portion 19may be formed separately from the flow path partition/vapor dischargeguiding plate 18 and joined to the flow path partition/vapor dischargeguiding plate 18. The guiding portion 19 may also be formed by bending aportion of the flow path partition/vapor discharge guiding plate 18towards the fin base 13. The guiding portion 19 projects to be tilted ata certain angle towards the fin base 13 from the vertically lowerportion of the fins 12 of the middle channel block 3 so as to contactwith the fluid supply pipe 10. Therefore, bubbles which were generatedfrom the fins 12 of the lower channel block 2 and have passed the fins12 are prevented from flowing into the middle channel block 3 because ofthe guiding portion 19 which works as an obstacle, and guided into thevapor discharge path 16. Similarly, because the guiding portion 19projects at a certain angle towards the fin base 13 from the verticallylower portion of the fins 12 of the upper channel block 4 so as tocontact with the fluid supply pipe 10, bubbles which were generated fromthe fins 12 of the middle channel block 3 and have passed the fins 12are prevented from flowing into the upper channel block 4 because of theguiding portion 19 which works as an obstacle, and guided into the vapordischarge path 16.

FIGS. 2A and 2B show an example of a structure of the fluid supply pipe10. FIG. 2A shows a fluid supply pipe 10 which includes, at a certaininterval on the side surface, a plurality of coolant supply holes havingdiameters which are gradually enlarged. Further, FIG. 2B shows anothercase where the fluid supply pipe 10 includes, on its side surface, acoolant supply slit having an opening area which is gradually enlarged.In either case, the opening diameter and the opening area are arrangedto be larger at a further downstream side of the coolant.

FIGS. 3A and 3B shows a structure of the flow path partition/vapordischarge guiding plate 18. FIG. 3A shows a front view and FIG. 3B showsa side view. The flow path partition/vapor discharge guiding plate 18 isformed by a pressed metal plate. Opening portions 18 a and 18 b arerespectively formed between the lower channel block 2 and the middlechannel block 3 and between the middle channel block 3 and the upperchannel block 4. Bubbles generated and growing in the lower channelblock 2 are discharged from the opening portion 18 a into the vapordischarge path 16. Similarly, bubbles generated and growing in themiddle channel block 3 are discharged from the opening portion 18 b intothe vapor discharge path 16.

A guiding portion 19 is formed at the edge of the opening portion 18 a,more specifically, at a vertically lower edge portion of the fins 12 ofthe middle channel block 3. Similarly, a guiding portion 19 is formed atthe edge of the opening portion 18 b, more specifically, at a verticallylower edge portion of the fins 12 of the upper channel block 4. Theguiding portion 19 may be formed by bending a portion of the flow pathpartition/vapor discharge guiding plate 18.

FIGS. 4A and 4B show an exploded perspective view of fins 12 and flowpath partition/vapor discharge guiding plate 18. Bubbles which aregenerated at the fins 12 in the lower channel block 2 collide into theguiding portion 19 and thereby, instead of proceeding into the middlechannel block 3, the bubbles are discharged from the opening portion 18a into the vapor discharge path 16. Bubbles which are generated at thefins 12 in the upper channel block 4 are directly discharged into thevapor discharge path 16.

FIG. 5 shows an overall structure of the ebullient cooling device 1. Thecooling portion 28, a main portion, is sandwiched between heating bodies26 such as a power device unit. Provided vertically beneath the coolingportion 28 are a coolant supply jacket 22 and a fluid distribution plate24. Coolant which is supplied from vertically below by a pump is storedand distributed in a sufficient amount to each fluid supply pipe 10 ofthe cooling portion 28. On the other hand, provided vertically above thecooling portion 28 is a vapor discharge jacket 30 which is connected tothe vapor discharge path 16 of the cooling portion 28. The bubblesdischarged into the vapor discharge path 16 by the guiding portion 19are collected at the vapor discharge jacket 30 to be discharged to theoutside.

By sandwiching the flow path partition/vapor discharge guiding plate 18between the fins 12 and vapor discharge path 16 in such a manner, thepresent embodiment can avoid the deterioration of heat transferperformance and reduction of the critical heat flux by preventingbubbles generated by each cooling channel block from proceeding into andgrowing excessively in the subsequent cooling channel block.

Further, in the present embodiment, as the vapor discharge path 16 isprovided on the top surface side of the fins 12, that is the oppositeside to the power device unit which is a heating body, the width of thecooling device can be shortened.

Furthermore, because the flow path partition/vapor discharge guidingplate 18 in the present embodiment can be simply positioned on the fins12, a simplification of the structure and enhancement of assemblabilityat the time of manufacturing can be achieved.

Further, the bubble discharging performance can be enhanced because ofbuoyancy by vertically installing the ebullient cooling device 1 andfins 12 as in the present embodiment.

It should be noted that an ebullient cooling device according to thepresent embodiment can be applied not only to inverter cooling devicesof hybrid vehicles but also to any heating bodies. Although the systemconfiguration of a cooling device according to the present embodimentcan be freely decided, examples are shown in FIGS. 6 and 7.

In FIG. 6, the gas-liquid two-phase flow discharged from the ebullientcooling device 1 is supplied to the gas-liquid separator 106. Connectedto the gas-liquid separator 106 is a condensor 108, which is furtherconnected to a second gas-liquid separator 110. The cooling fluid fromthe gas-liquid separators 106, 110 is supplied to a supercooler 102 viaan adjusting valve 112 and circulated to the ebullient cooling device 1by a pump 104. Connected between the adjusting valve 112 and thesupercooler 102 is an accumulator 100 which supplies the cooling fluidto the supercooler 102 by using a gas pressure.

In FIG. 7, the gas-liquid two-phase flow which is discharged from theebullient cooling device 1 is supplied to a condenser 108, to which thegas-liquid separator 116 is connected. The cooling fluid from thegas-liquid separator 116 is circulated to the ebullient cooling device 1by a pump 104. Connected between the pump 104 and the gas-liquidseparator 116 is an accumulator 100 which supplies the cooling fluid tothe pump 104 by using gas pressure.

1. An ebullient cooling device for cooling a heating body, comprising:at least first and second cooling channel blocks, both arranged in avertical direction, comprising: a cooling fin that causes coolant toflow in the vertical direction; a vapor discharge path formed on a sideof the cooling fin that is opposite to a side in contact with a heatingbody; a partition positioned between the cooling fin and the vapordischarge path; and an opening portion provided at the partition,between the first and second cooling channel blocks; a guiding portionprovided between the first and second cooling channel blocks, theguiding portion formed as a portion of the partition to project from anedge of the opening portion towards the heating body contacting side ofthe cooling fin, and guiding a bubble generated in the first coolingchannel block to the vapor discharge path by preventing the bubble fromproceeding into the second cooling channel block; and a fluid supplypipe provided between the first and second cooling channel blocks forsupplying the coolant to the second cooling channel block, wherein afront edge of the guiding portion contacts with the fluid supply pipe.2. The ebullient cooling device according to claim 1, wherein theguiding portion is formed, from the cooling fin of the second coolingchannel block, to be tilted towards the cooling fin of the first coolingchannel block. 3-5. (canceled)